The invention relates generally to printers, copiers and other image forming devices and, more particularly, to a sheet media alignment and offsetting system in which all sheets output by the printer are more reliably moved to the correct output position.
In many conventional printers and copiers, the paper or other sheet media is conveyed by rollers from the print engine to the output tray, sorter stacking trays or some other output device. (For convenience, printers, copiers and other image forming devices will be referred jointly as printers unless noted otherwise.) Some printers include an offsetting feature in which one document is offset from the prior document output to the same tray. If a user selects a printer""s offsetting feature, each sheet in a second document or print job is output to the output tray off set a predetermined distance to one side, usually about xc2xd, from the sheets in the previously output document or print job. Offsetting is used to separate multiple documents or print jobs output to the same tray.
For center justified printers in which an output side guide is not available for all paper sizes, position errors perpendicular to the transport direction can occur as paper is conveyed to the output device. This misalignment is sometimes referred to as xe2x80x9cskewxe2x80x9d and misaligned sheets are said to be xe2x80x9cskewed.xe2x80x9d Conventional offset devices assume a nominal center position for each sheet output from the print engine. Each sheet is moved right or left a predetermined distance from this position without regard to the actual position of the sheet. If a sheet is misaligned to this nominal position, then the alignment error is carried forward affecting the final sheet position. Hence, proper alignment is important to the offsetting feature to ensure that all sheets in a print job are output in an orderly stack and to ensure that the stack of sheets in each print job is properly offset from other print jobs output to the same tray.
The present invention is directed to sheet media alignment and offsetting devices and methods in which all sheets output by the printer are more reliably moved to the correct output position. In one embodiment, each sheet is moved to an xe2x80x9calignedxe2x80x9d position as it is conveyed through the alignment/offset mechanism and then, if offsetting is desired, the sheet is moved the desired offset distance from the aligned position to the correct offset position. Preferably, the aligned position is set to correspond to the correct non-offset output position so that each sheet is output to the correct position whether or not offsetting is used. In an alternative embodiment, each sheet is moved directly from the position it is received in the output device to either the aligned position for non-offset output or to the offset position for offset outputs